Temperature dependence longitudinal relaxation time

One further point needs to be mentioned when probing the feasibility of a particular experiment. Apart from its dependence on temperature and concentration (for instance of ions, solutes, impurities, isotopes), relaxation times - in particular the longitudinal relaxation time Tj - depend on the field strength. This can be understood from the concept that energy exchange is most efficient if the timescale of molecular motion is equal to the Larmor frequency. Often, molecular motion takes place over a wide range of frequencies, so that the func-... 

Figure 4. Temperature dependence of the longitudinal relaxation time of water in the water-NaLS system.

Fig. 13. Temperature dependence of longitudinal relaxation time tj of water present in phenolic foams in 25 Oe (A) and 400 Oe (B) fields (o, a, o, see legend to Fig. 12)H)...

The temperature dependence of Tj (Fig. 13) points to a noticeable effect of the nature of adsorbent (phenolic oligomer) on the properties of adsorbed water. Firstly, the value of Ti (1-1.2 s) is nearly half that of free water (in 0.5 1). Secondly, relaxation curves sharply differ in 20- and 400-oersted fields. In the 20-oersted field the dependence Ti = f (T) is stepwise and the steepest part is observed near temperatures corresponding to the phase transition water - ice . The authors suggest that the minimum observed between 0 to -2 °C is connected with the dispersion of the relaxation time distribution. In order to confirm this assumption a classical relaxation analysis using deuterated water and the temperature dependence of longitudinal relaxation time is required. 

For materials applications, the chemical shifts of methanol and ethylene glycol can be monitored in the liquid state to follow temperature [Hawl]. The most sensitive ehemical shift is the Co resonance of aqueous Co(CN)e with a sensitivity of 0.05 K at 7 T and 0.2 K at 2T [Dorl]. Furthermore, dibromomethane dissolved in a liquid crystal is a temperature sensitive NMR compound [Hed 1 ], and known phase-transition temperatures can be exploited to calibrate the temperature control unit [Hawl J. In temperature imaging of fluids, temperature can be determined from the temperature dependence of the selfdiffusion coefficient but convective motion may arise in temperature gradients [Hedl]. In the solid state, the longitudinal relaxation time of quadrupolar nuclei like Br is a temperature sensitive parameter [Suil, Sui2]. In elastomers, both T2 and Ti depend on temperature (Fig. 7.1.13). In filled SBR, T2 is the more sensitive parameter with a temperature coefficient of about 30 xs/K [Haul]. 

The temperature dependence of the longitudinal relaxation time tl is also an important quantity. For a Debye solvent, tl is given by the relationship... 

In general, care must be taken to recognize both intra- and intermolecular contributions to relaxation however, intermole-cular relaxation is often neglected in discussions of liquids at surfaces. With this assumption there is direct access to characterization of liquid dynamics at a surface (, 3,4). A study of the relaxation rate at different temperatures or frequencies provides a measure of the correlation time for water at the surface of a protein if the interproton distance, r, in the water molecule is known. The temperature dependence for longitudinal and transverse relaxation times predicted by equations 3 and 4 is shown schematically as the solid lines in Figure 1. At the position of the minimum in the longitudinal relaxation time, wTp is about 0.616 and Ti/To is about 1.6. 

Fluorine-labeled analogues of C. vinosum high-potential iron protein have been investigated by F NMR spectroscopy. By incorporation of specific fluorine-labeled amino acid residues, one can insert unique probes at well-defined locations within the protein core. The synthesis and purification of 2-, 3-, and 4-fluorophenylalanine (abbreviated 2-F-, 3-F-, and 4-F-Phe, respectively), 3-fluorotyrosine (3-F-Tyr), and 5-fluorotr3q)tophan (5-F-Trp) derivatives of C. vinosum HiPIP, the assignment of F NMR resonances, the measurement of longitudinal relaxation times, and the temperature dependence of F and resonances have all been reported 42, 43, 136). These measurements were used to examine structural perturbations of mutants, the dynamics of interaction of residues with the cluster, and solvent accessibility, and as a test of the relative contribution of cross-relaxation to magnetization decay. 

FIGURE 8.10 Temperature dependence of H atom longitudinal relaxation time for TVEX-TBP (1-groups CH2 -1, 2, 3 2-groups CH3-4), and TBP (3-gronp CH2-1 4-groups CH2-2, 3 5-group CH3-4). 

Magnetic resonance imaging (MRI) is one of the most effective NMR techniques in the clinical field (Caravan et al., 1999 Toth et al., 2004), which provides important information on damaged tissues in the living body. The lesonanee of water proton exhibits spin-lattiee (longitudinal) relaxation time (Ti) and spin-spin (transverse) relaxation time (T2) which depend on pH, temperature, and properties of their microenvironments (Lauffer, 1987). Marty kinds of Gd + complexes have already been employed as effective MRI contrast agents, because the... 

Figure 1. Schematic of the temperature dependence of the longitudinal and transverse relaxation times for water protons. Solid lines are predicted by Equations 3 and 4, while the dashed lines indicate the dependences often observed.

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